1. Field of the Invention
The present invention relates to a variable compression ratio internal combustion engine having a function that changes the compression ratio and a function that controls the strength of tumble flow in the combustion chamber of the internal combustion engine.
2. Description of the Related Art
In recent years, there has been proposed art capable of changing the compression ratio of an internal combustion engine for the purpose of improving fuel economy performance, output performance, and the like. Such art includes art in which a cylinder block and a crankcase are coupled with each other to enable relative movement therebetween, and camshafts are provided on the coupling portions thereof, the camshafts being rotated to cause relative movement between the cylinder block and the crankcase along the axial direction of the cylinder to change the volume of the combustion chamber and change the compression ratio of the internal combustion engine (for example, refer to the Japanese Patent Application Publication No. JP-A-2003-206771).
Another art has also been proposed in which a rocking member capable of rocking about a prescribed rocking center is linked to the part of a connecting rod that is divided into two that is linked to the crankshaft, the rocking center being moved by rotating the camshaft to change the volume of the combustion chamber and the stroke of the piston, thereby changing the compression ratio of the internal combustion engine (for example, refer to Japanese Patent Application Publication No. JP-A-2001-317383).
In the foregoing art, because the compression ratio is changed by changing the volume of the combustion chamber in the axial direction of the cylinder, if the compression ratio of the internal combustion engine is set low, the height of the combustion chamber is increased, and there are cases in which it is difficult to form a squish area within the internal combustion engine. When this occurs, it is not possible to sufficiently increase the speed of combustion in the internal combustion engine, and the thermal efficiency is decreased, leading to a tendency for knocking to occur.
With regard to this, yet another art has been proposed for causing a swirl controller to operate to increase the strength of swirl flow when the compression ratio is reduced (for example, refer to Japanese Examined Patent Application Publication No. JP-B-4-4458). However, in a variable compression ratio internal combustion engine in which the compression ratio is changed by changing the volume of the combustion chamber in the axial direction of the cylinder, because there is a change in the force in particular in the cylinder axial direction with respect to the intake flow, the influence of tumble flow, which is a vertical whirl, is greater than the influence of a swirl flow, which is a lateral whirl. Therefore, it could not be said that merely increasing the strength of the swirl flow enabled a sufficient improvement in the combustion condition under the condition of a low compression ratio. Further related arts have also been proposed in Japanese Patent Application Publications No. JP-A-2004-232580 and No. JP-A-2003-293805.